1. Field of the Invention
This invention relates to methods of making cutting blades and to the resulting blades; and more particularly it relates to methods of making extremely sharp surgical cutting implements out of vitreous materials and to the resulting surgical blades.
2. Prior Art
Many types of cutting blades are available to today's surgeons, but only a limited number of methods are used for manufacturing such blades. The sharper the blade, the narrower the incision that it will make, and the less pressure will be required to use it. As a result, the sharper the blade that is used, the less tissue trauma and bruising will result from each incision, and healing of the incision will be facilitated with less resulting scarring. Steel blades are presently most often used as scalpels for surgical procedures because of their durability, strength and relative sharpness, availability, moderate price, and also due to tradition, training and lack of alternatives. Steel cutting implements are made as they have been for decades using rolling or other flattening techniques, followed by grinding and honing. Nonetheless, scanning electron photomicrography demonstrates that many steel scalpels are surprisingly dull with edge rounding being seen at magnifications as low as about 30 to 100 times. By comparison, even ordinary steel razor blades are found to be about twice as sharp as commercially available disposable surgical scalpels. For this reason razor blade fragments have often been used for delicate surgical procedures, including eye surgery.
Honed diamond blades are also used as scalpels when fine incisions and delicate procedures are required. While photomicrographs show that diamond blades are substantially sharper than steel scalpels, having edge radii on the order of 100 angstroms, they are also more expensive and time consuming to produce than steel blades. U.S. Pat. No. 3,060,781 to Villalobos teaches one diamond cutter's approach to producing such a sharp diamond cutting tool. Methods of making honed aluminum oxide blades are taught by U.S. Pat. No. 3,543,402 to Seager.
Other non-metallic blades of superior sharpness have been formed from natural volcanic glass, such as obsidian, or from other vitreous, ceramic, or microcrystalline materials, using controlled fracturing methods of manufacture. In controlled fracturing methods, pressure is selectively applied to a block or a portion of a block of the material which has been selected for its shape, and fracturing of the material will then normally occur substantially along predictable angles from the vectors of applied force. When such force is applied to many naturally occurring vitreous or ceramic materials, such fracturing techniques will produce a much sharper edge than does steel honing or even diamond polishing because the edge produced by such fracturing is only a few molecules thick. However, traditional fracturing methods applied to traditional naturally occurring materials have not been applicable to the controlled production of cutting implements. This is due to the fact that cores or blocks of naturally occurring vitreous material, such as obsidian, will substantially always contain structural or molecular orientations (phenocrysts), imbedded stress fields caused by irregular cooling of the material at its time of formation, imperfections and inclusions (xenoliths), all of which are difficult to detect. These structural characteristics of naturally occurring vitreous materials will almost always cause fracturing along unpredictable lines or planes to produce cutting implements of unpredictable size and shape. Consequently, it is difficult to produce one or more blades of desired predetermined dimensions and configurations from naturally occurring vitreous materials. It is even more difficult to produce a series of blades which are all of predetermined size and shape from naturally occurring vitreous materials. While an occasional blade of desired dimension and configuration may be produced from natural vitreous material using standard fracturing techniques, much time and effort, and much of the core material may be wasted in this inefficient process.
Some mechanical processes for producing cutting implements from artificially produced vitreous material, such as glass, are known. Prior art which discloses methods for forming cutting edges from glass includes U.S. Pat. No. 3,207,398 to Forsstrom, et al. for a device for cutting glass plates to produce sharp edges; U.S. Pat. No. 3,819,096 to Pyper for glass knives; and U.S. Pat. No. 3,908,878 to Blum for microtome cutting edges. These, and all other prior art methods for forming cutting edges from artificially produced vitreous material, of which applicant is aware, involve the steps of scoring a glass block of given thickness, followed by force and pressure and fracturing of the block along the scored lines. Tafapolsky, et al. in U.S. Pat. No. 3,834,265 disclose techniques for producing ceramic (sapphire) razor blades and knives using microtome techniques followed by chemical sharpening. Glass and ceramic cutting implements which are produced using these prior art techniques are limited in length to the thickness of the glass block, can carry only one cutting edge per segment, cannot be produced in a manner which allows them to have a pointed or tapered end, and are always straight and cannot be produced with a curved cutting edge.
Honed glass razor blades may be produced according to U.S. Pat. No. 2,555,214 by Wallach, et al. which teaches a method of producing glass razor blades by the tedious steps of grinding followed by etching in extremely dangerous and toxic hydrofluoric acid. Again, glass cutting implements produced using this technique will carry only one cutting edge per segment, cannot be produced in a manner which allows them to have a pointed or tapered end, and are always straight and cannot be produced with a curved cutting edge.